EP1062668B1 - Adsorption means for radionuclides - Google Patents

Description

The invention relates to chitin / chitosan adsorbents in the nuclear industry and in nuclear power plants for removal of radioactive pollution from aqueous solutions, and especially of elements like cesium, uranium, plutonium, Americium, curium, etc. can be used. You can also for cleaning waste and drinking water from toxic Heavy metals, e.g. Lead, mercury, cadmium, bismuth, Chrome etc. can be used.

In the nuclear industry and in the operation of nuclear power plants creates a large number of liquid radioactive waste. These wastes pose a high health risk People and nature. The storage of such waste is very expensive and unreliable. To reduce the Risk of liquid radioactive waste is divided into one solid state transferred. Among many possible ways the adsorption process has great advantages. On The main advantage is that you can use it can achieve a significant reduction in volume. The Efficiency of the process depends on the quality of the Adsorbent. It has been found that chitin adsorbent have many useful properties.

Chitin is a natural polysaccharide containing amino sugar from (1,4) -linked 2-deoxy-2-acetamido-β-D-glucose (N-acetyl-D-glucosamine). Chitosan is a deacetylated derivative from Chitin. The high chemical and radiation stability of Chitin and chitosan make it possible to use these biopolymers Extraction of radionuclides from aqueous solutions use. The special properties of the Adsorption processes have been used for many different Radionuclides examined (Tsezos, 1980; Tsezos, Volesky, 1981; Muzzarelli, 1986; Muzzarelli et al., 1986, 1989, Ershov et al., 1992, 1993; Jansson-Charrier et al., 1994; Gorovoy, Kosyakov, 1994, 1996). Many of these jobs deal with deal with the study of extraction options of uranium.

The sorption properties of chitin and its derivatives have proven to be good enough to extract uranium from aqueous solutions in both cationic and in anionic form (Andreev et al., 1962). A effective method for extracting uranium from sea water in the use of chitin phosphate and chitosan phosphate found that give a very high degree of extraction (Sakaguchi Takashi et al., 1979 a, b, 1981). After this The method binds 1 g chitosan phosphate 2.6 mg uranium, if its Content in sea water is 2.8 mg. So it becomes a Extraction level of more than 90% obtained.

Cross-linked chitosan shows an increase in adsorption of metals, which reached 95%, this increase presumably based on the amino group content (Kim, Choi, 1985 a). Chitosan showed a better result than cross-linked chitosan (Kim, Choi, 1985 b). The adsorption of Uranium on chitosan, by the pH, the size of the Sorbent particles and the presence of other metals, has been studied (Jansson-Charrier et al., 1994). The maximum adsorption was achieved at pH 5, and up to 400 mg / l. A decrease in the size of the Sorbent particles showed a positive effect on the Kinetics of the sorption process, which is due to the limiting Diffusion factor indicates. The adsorption of uranium increased if carbonates and phosphates were present.

The kinetics (rate) of uranium adsorption on chitosan is slow. However, a significant improvement occurs when the chitosan becomes the chitosan phosphate or -Dithiocarbamate is modified. In this case, the Adsorption takes place in the first 15 minutes. The highest Adsorption indices for uranium were obtained with the derivative N- [2 (1,2-dehydrooxyethyl) tetrahydrofuryl] chitosan get that one Showed capacity of up to 800 mg / g (Muzzarelli et al., 1984).

The bioadsorption of uranium also occurs very easily in the Chitin of the cell walls of fungi, especially Rhizopus arrhizus, on (Tsezos, Volesky, 1982 a; Tsezos, 1983). It it was shown that at a pH of 2 to 3 to 4 hours of equilibrium is reached, and during this time 1 mg uranium adsorbed per 1 g cell wall becomes. At a pH of 4, up to 180 mg of uranium can be in the Cell walls are adsorbed while adding pure chitin this pH only absorbs 6 mg / g uranium, although the Mushroom cell walls do not consist of 100% chitin.

The use of chitin for cleaning with radioactive Substances, especially plutonium, contaminated water, can be a solution to the problem encountered during the Extraction, enrichment and use of nuclear fuels neutralize generated waste. The contact between Chitin particles and radioactive liquid is separated by a multi-stage mixing and settling, countercurrent process and passed through towers. The purified water and the contaminating chitin are removed with the help of Gravity separation or filtration separated. Under Using this procedure can make up over 80% plutonium aqueous solutions with a pH between 5 and 10 can be extracted (Silver, 1978).

It is known that chitin and the chitin-containing one Material Chisit-03 Plutonium (IV), Americium (III) and Curium (III) extracted effectively. The distribution coefficients rise in order: Pu (IV) <Cm (III) <Am (III). The Adsorption of Pu (V) and Pu (VI) by Chisite-03 is considerably better than the adsorption by chitin, and is comparable to the adsorption of Pu (IV) (Ershov et al., 1992 a).

It has the high radiation stability of chitin and chitosan made the investigation of these materials possible Concentration of waste water from nuclear fuels (radioactive Isotopes of cesium, zirconium, hafnium and other elements) from water circulating in reactor cooling systems, perform. Cesium, like other alkali metals, turns on Chitin and chitosan not adsorbed. From the others Nuclear fission elements have been studied Rare earth elements such as cerium, europium, thulium and terbium, carried out (Muzzarelli et al., 1972; Lopez de Alba et al. 1988 a). The degree of extraction (%) of these metals on chitin was low: between 3 and 9%. Chitosan showed better ones Results, although these were also not high: between 30 and 45%. The extraction of ruthenium from wastewater from the Nuclear power plant at Marcoulle also showed low Results. Up to 2 and 4% of this metal was found in chitin adsorbed, and in chitosan up to 60% (Muzzarelli, 1970, 1977). Chitin / chitosan-containing mushroom material (higher basidiomycetes) showed for uranium, plutonium, Americium, curium and heavy metals better Adsorption results (Gorovoj, Kosyakov, 1994, 1996; Kosyakov et al., 1997).

The use of a chitin adsorbent for extraction of radionuclides from aqueous solutions was in this Promising in terms. But there are still unsolved Problems in this area that do not allow the Chitin adsorbent to be used industrially. The Main problem is that it is not possible Cesium isotopes from liquid radioactive waste water too remove. Cesium is a major component in the radioactive contamination of both liquid waste in nuclear technology as well as in nuclear power plants. Another The disadvantage of the known chitin adsorbents is that low efficiency of extraction of plutonium ions and other radionuclides from liquid waste. These disadvantages practically do not allow the problem of cleaning to dissolve liquid radioactive waste.

The object of the present invention was therefore to Adsorbents for radionuclides, e.g. cesium, Transurans, etc., with which the previous problems can be resolved.

This object is achieved with the present invention solved.

The invention relates to an adsorbent Claim 1.

Preferred embodiments thereof are the subject of Claim 2.

Another object is a method according to claim 3 for Production of the adsorbent according to the invention.

Preferred embodiments thereof are the subject of Claims 4 and 5.

Another subject is also a method according to claim 6 for cleaning liquid, salt-containing radioactive Waste.

Preferred embodiments of this method are Subject matter of claims 7 and 8.

Another subject is the use of a Adsorbent according to the invention for cleaning radioactive waste, especially from the nuclear industry and of nuclear power plants.

According to the present invention, the mushrooms (higher basidiomycetes) obtained chitin-containing Material given new properties to radioactive cesium adsorb from water and concentrated salt solutions. According to the invention, it is also possible Adsorption properties of a chitin-containing material with regard to such radionuclides, e.g. Uranium, Plutonium, Americium, Curium, to improve considerably.

According to the invention this is achieved in that Ferrocyanides of the transition metals in the form of microcrystals within the matrix and on the surface of hairdressers of a chitin Material, e.g. Copper ferrocyanide it convert to a microcrystalline insoluble state. At the expense of their reactive groups, they become new ones Adsorbent that is capable of dealing with radioactive Connect cesium. Loosen the ferrocyanide microcrystals the adsorbent matrix and increase its surface area, and improve the access of a solution to the reactive Centers of chitin.

A chitin-containing material for the manufacture of a Adsorbent from natural or cultivated mushrooms (higher basidiomycetes) is described in Russian patent 2073015 (Gorovoj, Kosyakov, 1997).

To a chitin-containing material versus radioactive To impart cesium adsorption properties suggested additional reactive groups incorporate that are effective to deal with this chemical Connect element. To the adsorption properties in With regard to increasing plutonium or other radionuclides, it is proposed to contact Heavy metal ions with reactive centers of chitin too increase by looking at the structure of the chitin-containing Material loosens.

According to the invention, preferably ferrocyanides of transition metals are proposed as modifying substances. Ferrocyanides include normal salts (e.g., Me ₂ Fe (CN) ₆ ), and mixed salts, [M _4-2x Me _x Fe (CN) ₆ }, where M is a monovalent metal cation and Me is a divalent cation of a transition metal. Ferrocyanides of transition metals show high selectivity for ions from heavy alkali metals, including the radioactive isotopes of cesium. Copper ferrocyanide has several advantages compared to ferrocyanides on other metals. It has the lowest solubility (approximately 10 ^-5 mol / l) and the highest partition coefficient for cesium (K _d = 5.10 ⁵ ).

Red = Reduktionsmittel
Ox = OxidationsmittelInsoluble ferrocyanides of transition metals can be obtained by direct precipitation as a result of the reduction of suitable soluble ferrocyanides according to the following reaction equation:

Red = reducing agent
Ox = oxidizing agent

Chitin-containing materials have certain Reduction properties.

If K ⁺ and Fe (CN) ₆ ^4- ions are present, the reaction can lead to the formation of various compounds:

So that the reaction leads to (1), the ratio of Cu ²⁺ and Fe (CN) ₆ ^4- of 1: 2 must be maintained, and the reaction in an ammoniacal solution with an ammonia concentration of 0.1 to 2 mol / l be performed. It has been experimentally confirmed that the preferred concentration of ammonia in a solution is in the range of 0.3 to 0.7 mol / l.

The chitin containing described in Russian Patent 2073015 Material represents a chitin-glucan-melanin complex natural biopolymer from a cell wall of Mushrooms (higher Basidiomycetes). The material has one fine-fiber structure. Chitin is in the form of Microfibrils with a diameter of 150 to 250 Å and a length of up to 1 to 2 µm. The chitin microfibrils are within the amorphous glucan-melanin matrix, thereby maintaining a microfibrils spatial network structure is ensured. At the same time, the glucan-melanin complex prevents you direct contact of chitin microfibrils with the solution, which increases the effectiveness of the extraction of radionuclides, such as e.g. Uranium, plutonium, americium, curium, etc., and Heavy metals, is reduced.

According to the invention, this disadvantage is avoided and the contact of a solution with chitin microfibrils is improved by loosening the glucan-melanin matrix by introducing ferrocyanide microcrystals into the matrix mass. To achieve this, the material is impregnated with soluble salts containing Cu ²⁺ and Fe (CN) ₆ ^3- , and then a reduction is carried out. In order to realize the implementation, it is necessary to add ammonia to the suspended material. Inside and on the surface of the glucan-melanin matrix, microcrystals of copper ferrocyanide are formed, which loosen the matrix.

The invention will now become more apparent with the following examples illustrated, but not limited to:

example 1

The starting material for the preparation of an adsorbent was made from mycelial mass of the Basidiomycete mushroom Coltricia perennis (L .: Fr.) Murr. receive. For this purpose, the dry fruiting body was cleaned of the sand, cut into pieces and ground to a homogeneous mass. 1 kg of dry biomass was placed in 10 l of a 10% aqueous NH ₃ solution and subjected to a temperature of 20 ° C. and constant comminution for one hour. Then the solid mass was separated from the liquid and washed five times with pure water in 15 l portions. The chitin-containing material obtained is suitable for producing an adsorbent.

The washed material was suspended in water (1:75 ratio). 3.3 molar equivalents of Cu ²⁺ and 2.2 molar equivalents of Fe (CN) ₆ ^3- per 1 kg of the dry material were then added to the suspension. This mixture was subjected to homogenization (crushing) for one hour, and ammonia was added to obtain a solution of 0.5 mol / l. The suspension was then subjected to a two-hour homogenization. The adsorbent obtained by separating from the liquid was washed three times with pure water and then dried. It contained 1.1% Cu ₂ Fe (CN) ₆ on the surface and inside of the fibers.

Example 2

The starting material for the preparation of an adsorbent was obtained from the mycelial mass of the basidiomycete fungus Coriolus hirsutus (Wulf .: Fr) Quel. For this purpose, the dry fruiting body was debarked, cut into pieces and ground to a homogeneous mass, 1 kg of dry biomass was placed in 15 l of a 10% aqueous NH ₃ solution and at a temperature of 20 ° C. and a constant homogenization for two hours subjected. The solid mass separated from the liquid was washed five times with pure water in 15 l portions. The chitin-containing material obtained is suitable for producing an adsorbent.

The washed material was suspended in water (1:25 ratio). 3.3 molar equivalents of Cu ²⁺ and 2.2 molar equivalents of Fe (CN) ₆ ^{3- were} added to the suspension (for 1 kg of the dried material). This mixture was subjected to homogenization for 1 hour and ammonia was added to obtain an ammoniacal solution of 0.4 mol / l. The suspension was then subjected to a two-hour homogenization. The adsorbent obtained was separated from the liquid, washed three times with pure water and dried. It contained 0.13% Cu ₂ Fe (CN) ₆ on the surface and inside the fibers.

Example 3

The starting material for the preparation of an adsorbent was obtained from the mycelial mass of the Basidiomycete fungus Coriolus versicolor (L .: Fr) Quel. For this purpose, the dry fruiting body was freed from the bark, cut into pieces and ground to a homogeneous mass. 1 kg of dry biomass was placed in 20 l of a 10% aqueous NH ₃ solution and subjected to a temperature of 40 ° C. and constant homogenization for four hours.

The solid mass separated from the liquid was five times washed with pure water in proportions of 15 l each. The Chitin-containing material obtained is for production an adsorbent.

The washed material was suspended in water (1:75 ratio). Then 10 molar equivalents of Cu ²⁺ and 6.6 molar equivalents of Fe (CN) ₆ ^{3- were} added to the suspension (for 1 kg of the dried material). This mixture was subjected to grinding for one hour, and then ammonia was added to obtain an ammoniacal solution of 0.6 mol / l NH ₃ ⁺ . The suspension was then subjected to a two-hour homogenization. The adsorbent obtained was separated from the liquid, washed three times with pure water and dried. It contained 3.2% Cu ₂ Fe (CN) ₆ on the surface and inside the fibers.

Example 4

The starting material for the preparation of an adsorbent was obtained from the mycelial mass of the Basidiomycete mushroom Coriolus zonatus (Nees: Fr) Quel. For this purpose, the dry fruiting body was freed from the bark, cut into pieces and ground to a homogeneous mass. 1 kg of dry biomass was placed in 10 l of a 15% aqueous NH ₃ solution and subjected to a temperature of 60 ° C. and constant homogenization for two hours. Then the solid mass separated from the liquid was washed five times with pure water in 15 ml portions. The chitin-containing material obtained is suitable for producing an adsorbent.

The washed material was suspended in water (1:25 ratio). Then 10 mol equivalents of Cu ²⁺ and 6.6 mol equivalents of Fe (CN) ₆ ^{3- were} added to the suspension (for 1 kg of the dried material). This mixture was subjected to homogenization for 1 hour, and then ammonia was added to obtain an ammoniacal solution of 0.9 mol / l. The suspension was then subjected to a two-hour homogenization. The suspension medium obtained was separated from the liquid, washed three times with pure water and dried. It contained 1.0% Cu ₂ Fe (CN) ₆ on the surface and inside the fibers.

Example 5

The starting material for the preparation of an adsorbent was obtained from the mycelial mass of the Basidiomycete mushroom Daedalea Quercina (L: Fr) Quel. For this purpose, the dry fruiting body was freed from the bark, cut into pieces and ground to a homogeneous mass. 1 kg of dry biomass was placed in 10 l of a 20% aqueous NH ₃ solution and subjected to a temperature of 80 ° C. and constant homogenization for two hours. The solid mass separated from the liquid was washed five times with pure water in 15 l portions. The chitin-containing material obtained is suitable for producing an adsorbent.

The washed material was suspended in water (1:75 ratio). 15 molar equivalents of Cu ²⁺ and 6.6 molar equivalents of Fe (CN) ₆ ^{3- were} added to the suspension (for 1 kg of the dried material). This mixture was subjected to homogenization for 1 hour and ammonia was added to obtain an ammoniacal solution of 0.5 mol / l. The suspension was then subjected to a two-hour homogenization. The adsorbent obtained was separated from the liquid, washed three times with pure water and dried. It contained 11.2% Cu ₂ Fe (CN) ₆ on the surface and inside the fibers.

Example 6

The adsorbent properties of the adsorbents obtained (Examples 1 to 5) were checked in a static manner. For this purpose, a model solution of the isotope Cs-137 with an activity of 2.10 ⁷ Ci / l in drinking water with a pH = 5-7 was prepared. 20 mg of an adsorbent were added to 400 ml of the solution and then kept under constant homogenization. The concentration of Cs-137 in the solution was determined over a predetermined time (1, 3, 15 and 30 days) and the partition coefficient (K _d ) was calculated using the formula: K _d = (A _s .V _aq ) / (A _aq .M _s ), where A _s and A _aq mean the activity of the radionuclide in the adsorbent or the aqueous phase, V _{aq is} the volume of the aqueous phase in ml, and M _{s is} the weight of the air-dried adsorbent in g.

The results are shown in Table 1. Cu ₂ Fe (CN) ₆ content (%) Cs-137 partition coefficient ml / g, after days Examples 1 3 15 30 1 1.1 1.0x10 ⁴ 2.4x10 ⁴ 0.6x10 ⁵ 1.0x10 ⁵ 2 0.13 0.6x10 ⁴ 0.9X10 ⁴ 0.2x10 ⁵ 0.2x10 ⁵ 3 3.2 1.5x10 ⁴ 3.4x10 ⁴ 1.2x10 ⁵ 1.0x10 ⁵ 4 1.0 1.2x10 ⁴ 2.6x10 ⁴ 0.8x10 ⁵ 1.2x10 ⁵ 5 11.2 1.8x10 ⁴ 4.1x10 ⁴ 1.3x10 ⁵ 1.3x10 ⁵ Chitin-containing materials without Cu ₂ Fe (CN) ₆ showed practically no adsorption properties with respect to Cs-137. Under the same experimental conditions, the partition coefficients did not exceed 28.

Example 7

The adsorbent according to Example 5 was tested on real liquid radioactive waste which was formed during the operation of a nuclear power plant. These are specific wastes that differ in the high content of various salts. Known adsorbents for radioactive cesium are not effective in concentrated salt solutions. The tests were carried out on columns with a volume of 100 ml, into which 10 g of the adsorbent were added. The liquid feed rate was one column volume in one hour. The pH of the solutions was adjusted to 5 to 7. Radioactivity measurements were made after filtration of liquid in an amount of 100 column volumes. The results of the extraction of radioactive cesium from water and saline solutions are shown in Table 2. Salinity g / l Cs-134 + Cs-137, radioactivity, Ci / l Cleaning (%) scraps initial value full scale 1 <0.1 3.2x10 ^-6 1.9x10 ^-10 99.994 2 2.06 2.6x10 ^-7 1.8x10 ^-9 99.3 3 10.4 8.3x10 ^-5 2.4x10 ^-8 99.97 4 11.2 4.2x10 ^-4 1.9x10 ^-7 99.95 5 107 6.0x10 ^-3 1.8x10 ^-8 99.9997 6 240 6.1x10 ^-6 1.0x10 ^-9 99.98 7 317 5.3x10 ^-4 4.7x10 ^-8 99.991 8th 446 2.3x10 ^-4 2.1x10 ^-8 99, 991

The extraction of radioactive cesium from these solutions by a chitin-containing material without Cu ₂ Fe (CN) ₆ did not exceed 6%.

Example 8

Adsorbent exchange capacity tests were conducted with real liquid radioactive waste from a nuclear power plant. The content of salts in the solution was 317 g / l (Example 7, Table 2). The pH of the solutions was adjusted to 6. The experimental conditions were similar to those in Example 7. 700 column volumes of filtered liquid were passed through a column with the adsorbent. The measurements of the Cs-134 + Cs-137 activity were carried out after every 100 volumes of the filtered solution. The results are summarized in Table 3. Column volumes Degree of radioactivity after filtration, Ci / l 0 (initially) 5.3x10 ^-1 100 4.7x10 ^-5 200 1.8x10 ^-7 300 2.5x10 ^-7 400 3.7x10 ^-7 500 7.6x10 ^-7 600 1.3x10 ^-7 700 1.7x10 ^-7

This experiment shows the reliability of the Adsorbent according to the invention in a concentrated Saline. Even after filtering 700 column volumes such a solution will require cleaning of more than 99.9% (Removal of radioactive cesium). It surpasses the effect of all known adsorbents.

Example 9

Chitin-containing material obtained from the mushrooms of Examples 1 to 5 has adsorbent properties with respect to uranium, plutonium, americium, curium, etc. (Gorovoj, Kosyakov, 1997; Kosyakov et al., 1997). The sorbent obtained according to the invention considerably exceeds the starting material with regard to the distribution coefficients of the radioactive transuranic elements. Solutions with Pu-239 and Am-241 were used for the experiments. The radioactivity of the initial solutions was 1000 Bq / l. The salt content was set at 60 g / l. The pH of the solutions was adjusted to 6.5. The extraction of the radionuclides was carried out in a static manner. 500 mg of a chitin-containing material or 500 mg of the adsorbent according to the invention were added to 50 ml of a radioactive solution. The suspension was mixed for 30 minutes, centrifuged and the radionuclide content in the liquid phase determined. The distribution coefficient (K _d ) was calculated using the formula (see Example 6). The results are shown in Table 4. Adsorption medium K _d , ml / g Pu-239 Am-241 Chitin-containing material 1500 5900 Adsorbent (invention) 8400 15000

Claims (9)

1. An adsorbent for radionuclides and heavy metals on the basis of a fine-fibered chitin-containing material obtained from natural fungi or fungi obtained by culture (higher basidiomycetes),
   characterized in that
   said adsorbent contains insoluble ferrocyanide of the transition metals in the form of microcrystals inside the matrix and on the surface of fibers of a chitin-containing material.
2. Adsorbent according to claim 1,
   characterized in that
   the insoluble ferrocyanide is copper ferrocyanide.
3. A process for manufacture of the adsorbent according to claim 1 or 2,
   characterized in that
   a chitin-containing mass is impregnated with Cu²⁺ and Fe(CN)₆ ^3- salts and then converted into a microcrystalline insoluble state in an ammoniacal medium.
4. Process according to claim 3,
   characterized in that
   the ration of Cu²⁺ to Fe(CN)₆ ^3- is 1:2.
5. Process according to claim 3,
   characterized in that
   it is performed with an ammonia concentration of 0.1 to 2 mol/l, preferably with an ammonia concentration of 0.3 to 0.7 mol/l.
6. Process for cleaning of salt-containing radioactive effluents,
   characterized in that
   an adsorbent according to claim 1 or 2 is used and the cleaning process is performed in an column, statically or in another manner.
7. Process according to claim 6,
   characterized in that
   the contact time of the adsorbent with a solution to be cleaned is no less than 5 minutes, preferably 30 to 120 minutes.
8. Process according to claim 6 or 7,
   characterized in that
   the pH value in the solution to be cleaned is set to 3 to 11, preferably to 5 to 8.
9. Use of an adsorbent according to claim 1 or 2 for cleaning of radioactive effluents, in particular from the nuclear industry and from nuclear power stations.